Chart 3 - B0285 - Electric Rear Defrost Circuit Low

Schematic:

CIRCUIT DESCRIPTION
When the rear defog input circuit 292 to the Body Control Module (BCM) is momentarily switched to ground (as when the rear defog switch is pressed), the BCM will respond by grounding circuit 193, the coil of the rear defog relay.

This action energizes the rear defog relay providing power to circuit 293-rear defog heater elements. Circuit 193 also provides ground through the BCM for the rear defog ON/OFF indicator. The first time in an ignition cycle the rear defog is activated, rear defog will remain On for 15 minutes or until the ignition switch is turned Off. If the rear defog is activated again during the same ignition cycle, rear defog will remain On for 7 1/2 minutes or until the ignition switch is turned Off. Pressing the rear defog button before the timer has expired will turn the rear defog function Off.

DTC PARAMETERS
^ Ignition in RUN
^ Circuit 193 is shorted-to-ground or
^ Rear defog is requested and circuit 193 is open

DIAGNOSTIC AIDS:
^ Check for poor connection at the BCM. Inspect harness connectors for backed out terminals, improper terminal mating, broken connector locks, improperly formed or damaged terminals and poor terminal to wire connection (terminal crimped over wire insulation and not conductors).
^ Inspect wiring harness for damage. Check for broken or chaffed insulation.
^ If fault is suspected to be intermittent, wiggling harness wiring may help in locating fault.

TEST DESCRIPTION

Diagnostic Chart: